As integrated circuits become more complex many of them contain modules connected to a common internal communication bus. In the operation of the circuit each module makes a request for access to the bus to a controller when it wants it and the controller allocates the use of the bus to the module having the highest priority. This method of operation is satisfactory in practice, but it suffers from the disadvantage that a user observing the operation of the circuit by monitoring the signals on its contact pins does not know which module is using the bus at the time. For example, if the bus is brought out at contact pins of the circuit and through them is connected to access external memory, it will not be clear which module is making a memory access, as a memory access appears the same regardless of the module making it. This information would clearly be useful in debugging software or otherwise looking for the cause of a failure of a system to work correctly.
It is an object of the present invention to provide a solution to this problem.